The purpose of an over-voltage protection circuit is to protect sensitive electronic circuitry from damage or stress that may result from the application of a voltage that exceeds a preset tolerance range. Such over-voltage protection circuits, sometimes referred to as “surge protectors,” are common in the realm of consumer electronics. Frequently, electronic devices, such as televisions, stereos, or PCs are plugged into such surge protection circuits which are connected directly to a wall socket. During operation, if the wall socket voltage rises above a preset value (e.g., 125 volts) due to an electrical spike, the surge protector will clamp or otherwise short the excess voltage to ground, preventing the line voltage from rising above the preset value, and thereby protecting the connected devices from damage.
Integrated circuits are similarly prone to damage from over-voltage conditions, but tend to be far more sensitive to voltage spikes. This is largely due to the fragile nature of the integrated circuit components themselves, which are constructed from very thin layers of semiconductor material which are easily damaged by voltage levels that exceed a relatively narrow tolerance range. Further exacerbating this problem is the trend toward lower power, higher density semiconductors, which require smaller, and thus increasing fragile, discrete components.
In the past, several approaches have been attempted to address this problem. One approach has involved the use special high voltage fabrication techniques for portions of the input circuitry that are exposed directly to external voltage supplies. These components, such as pass transistors and diodes, are specially fabricated to tolerate high voltages and serve to isolate other sensitive circuitry form direct exposure to external voltage sources, and thereby prevent damage.
This approach, however, is not optimal, because the fabrication of high voltage input components, such as high voltage ESD cells, is costly due to the necessary process variations required to create these circuits and further because such high voltage components tend to consume large areas of valuable die space. In addition, this approach may result in the semiconductor manufacturer having to produce multiple versions of the same device, i.e., one which can tolerate high input voltages and one which operates within normal input voltage parameters, increasing overall production cost and complexity.
Accordingly, it would be desirable to provide circuits and methods for over-voltage protection that do not require special high voltage components disposed on the integrated circuit.